JPH0230160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regulating and stabilizing the intensity of emitted X-rays from an X-ray source.

The intensity of the emitted X-rays is stabilized by forming a feedback signal for regulating the anode and/or filament voltage from the anode voltage and/or the anode current or from an amount proportional thereto.

The present invention also relates to an X-ray source (X-ray generator) to which the above method is applied.

This X-ray source has an anode, a cathode, a voltage source,
Includes filament power supply. At least one of these power sources is provided with controllable means for forming the electrical quantity acting on the x-ray tube. This controllable means forms a quantity of electricity from the power supply voltage, to which the quantity of electricity acting on the x-ray tube is proportional. The radiation intensity of an x-ray source, including an x-ray tube with an anode and a cathode, depends on the high voltage between the anode and cathode and on the anode current. On the other hand, the anode current mainly depends on the thermionic emission of the cathode filament and therefore on the filament voltage. The intensity of the emitted X-rays is thus influenced by the anode voltage, the filament voltage, or both.
In many actual applications, it is important which of the above-mentioned quantities has an influence on which. This is because each has a different effect on the radiation characteristics.

The anode voltage mainly determines the photon energy distribution and the radiation transmittance. The anode current, on the other hand, controls the number of photons in a given period of time. Apart from the peak and average voltage levels, the waveforms of these voltages have a significant effect on the given x-ray radiation.

It is well known that in certain medical X-ray diagnostic applications it is advantageous if the anode voltage is as direct a voltage as possible. A practical method for smoothing the anode voltage and making the anode and filament voltages adjustable is to first replace the supply voltage to the X-ray equipment with an unregulated DC voltage;
It is then converted to an adjustable voltage by suitable controllable means. This adjustable DC voltage is converted to an AC voltage with appropriate frequency and amplitude.

The anode voltage is created from this AC voltage by a voltage doubler including capacitance and a rectifier. Although partially similar systems may be used, the output voltage of the DC-AC converter is applied to the filament of the x-ray tube via a suitable isolation transformer.

In the above system, the anode voltage and current (filament voltage) are set by adjusting the DC voltage. These voltages can be stabilized, in which case the anode voltage current is in principle constant. Another way to stabilize the anode voltage is to use a single control loop that takes the feedback signal directly from the anode voltage. In practical application, the above system has the following drawbacks.

First of all, the anode voltage current is not constant even if the DC-AC converter and the supplied DC voltage are stabilized. This is because certain components between the stabilization circuit and the x-ray tube are sensitive to heat.

Second, when using direct feedback from the x-ray tube, the control speed must be set slowly to stabilize the control loop. However, when such slow control is performed, the power supply frequency ripple contained in the unregulated DC voltage appears on the high voltage side, and it takes a very long time for the high voltage side to rise after switching on. In other words, the initial startup of the X-ray tube is poor, which is undesirable from a practical standpoint.

Conversely, if the control speed of the single control feedback loop control is set to a fast speed that does not cause power frequency ripples or voltage fluctuations on the high voltage side, the initial startup can be made faster, but the There are drawbacks such as overshoot and hunting caused by rapid control due to voltage fluctuations, which make it difficult to regulate and stabilize the X-ray intensity.

In view of the above-mentioned circumstances, the present invention has been developed to speed up the start-up at the time of initial operation to prevent power frequency ripples from appearing on the high voltage side, while at the same time
It is an object of the present invention to provide a method for regulating and stabilizing the intensity of emitted X-rays from an X-ray source, which can reliably regulate and stabilize the radiation intensity, and an X-ray source using this method.

A method for regulating and stabilizing the intensity of emitted X-rays from an X-ray source according to the present invention, which has been made to achieve the above object, regulates the intensity of emitted X-rays from an X-ray source and A method for stabilizing the intensity of emitted X-rays, the method comprising: receiving a first feedback signal from the output of a controllable means for variably controlling the amount of electricity supplied to the X-ray source from the amount of electricity supplied from a power source; and controlling the controllable means by a differential signal based on a comparison between the first feedback signal and a provisional reference signal set at a lower level than a reference signal corresponding to a desired amount of electricity to be supplied to the X-ray source. controlling said anode voltage and/or filament voltage from an anode voltage and/or filament voltage of said X-ray source that is proportional to the output of said controllable means or a quantity proportional thereto; This second feedback signal is compared with the reference signal set to a higher level than the provisional reference signal, and when the two values match, the inner feedback control circuit The signal to be compared with the first feedback signal is switched from the provisional reference signal to a differential signal based on the comparison between the reference signal and the second feedback signal, and the anode voltage and/or filament voltage is changed to the reference signal. A time constant of the inner feedback control circuit is set to be smaller than a time constant of the outer feedback control circuit, so that during initial operation, the inner feedback control circuit Further, during steady operation, the anode voltage and/or filament voltage is controlled by an external feedback control circuit.

To summarize this in other words, the method of the present invention uses a stabilizing device similar to a follow-up control system to stabilize the anode voltage supply, including controllable parts on both the inner and outer sides, with the inner control system input the outer control circuit is operated quickly to compensate for line frequency ripples and voltage variations in the voltage, and the outer control circuit has a sufficiently smaller time constant than the inner control circuit for proper stabilization; Furthermore, when the radiation source is activated, a temporary reference signal (temporary reference signal) is connected to the inner control circuit by bypassing the outer control circuit,
The purpose is to speed up the final balancing of the system.

Furthermore, the radiation source according to the present invention can be summarized as follows:
The control input of said controllable part is connected to the output of a comparator, one input of which is connected by suitable feedback means to the output of the controllable part. Also, one other input is connected to the output of a second comparator, one input of which is connected to a suitable feedback circuit for producing a feedback signal from the electrical quantity acting on the x-ray tube. , the other input is connected to the signal source.
This signal is made proportional to the desired amount of electricity to the x-ray tube.

Hereinafter, specific examples of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows the control principle of the stabilization method of the present invention, and FIG. 2 is a block diagram showing an example in which the intensity of X-rays is stabilized by the method of the present invention. FIG. 3 shows, corresponding to FIG. 1, how the high voltage and filament voltage are created in the X-ray source and how the feedback is created, respectively. FIG. 4 shows how the control signals are generated in the X-ray sources of FIGS. 2 and 3.

In FIG. 1, the high voltage of the X-ray tube and the filament voltage (current) are created by two cascade processes H ₁ and H ₂ . From the output amounts of S ₁ and S ₂ in the process, the feedback device of F ₁ and F ₂
Create feedback signals of f ₁ and f ₂ . f ₁ and f ₂ are feedback signals of internal feedback circuit H ₁
It is sent to comparators C ₁ and C ₂ to control f ₁ . Feedback signal f ₁ from feedback circuit F ₁ to comparator C ₁ controls process H ₁ . The feedback signal f ₁ of the inner control circuits H ₁ and F ₁ is compared with the output signal of the comparator C ₂ . The difference between the signal r of the reference source R and the feedback signal _f2 of the outer control circuit is proportional to the output signal of the comparator _C2 . The outer control circuit is bypassed by a switch K which switches the signal r' of another reference source R' into the reference signal of the comparator _C1 . The X-ray sources in Figures 2, 3 and 4 are connected to a 300V external power supply. The main AC voltage passes through 302 and 303 to switch 301
It is connected to the high voltage power supply unit 10 and the filament power supply unit 230 by. The main body of the device is connected to ground potential by a connection 304. High voltage power supply unit 10 includes a switch 11, a rectifier 12, and a filter capacitor 13. The output voltage 15 is supplied to a controllable part VR, 20 which includes switching means 21, a diode 23, a chain 24 and a capacitor 25. Output voltage 2 of controllable unit 20
6 depends on the duty cycle (use cycle) of the switching means 21 which opens and closes periodically in response to the input voltage 15. The switching means 21 may be, for example, a switching transistor, in which case the controller 22 has suitable insulation, amplification and shaping means to adapt the pulses obtained from the pulse width modulator 70PWM to the switching transistor. It shapes the waveform. The output voltage 26 of the controllable section 20 is a DC-AC converter V
1,30. This converter V1,3
0 includes switching means 31 and 32 for periodic on-off switching with alternating phases, their controller 33, and a push-pull transformer 34. DC-AC converter 30 is controlled by pulses from pulse source 60b. The secondary winding of the transformer 34 has two parallel connected voltage doublers 40 with alternating phases.
A voltage is supplied to a and 40b. two pressure doublers 40
One of the voltage doublers 40 a and 40 b generates a positive high voltage with respect to the ground, and this voltage is connected to the anode 51 of the X-ray tube 50 . Similarly, the other voltage doubler 40b produces a negative high voltage, which is connected to the cathode 52. The two voltage doublers 40a, 40b include two cascades of capacitors Ci, Ci and a rectifier Dij connected to each other. A DC voltage 235 is generated from the main current in a filament power supply unit FP230 that includes a transformer 231, a rectifier 232, a filter capacitor 233, and a switch 234. This DC voltage is supplied to the controllable part FR240, which includes a series transistor 241. The stabilized DC voltage 245 is connected to the switching means 25
1,252, DC-AC converter FI, 250 including controller 253, push-pull transformer 254
is supplied to Switching means 251, 252
receives periodic alternating phase pulse control from pulse source 60c by control 253. The AC voltage obtained from the secondary winding of the transformer 254 is supplied directly to the filaments 52, 53 of the X-ray tube 50 to create a filament voltage.

A feedback signal 85 is generated from the regulated DC voltage 26 by feedback means VR, FB, 80. This means 80 includes a resistor 81, a phototransistor 83 optically coupled to a light emitting diode LED, 82, and a resistor 84. The high voltage feedback signal 105 is transmitted to the feedback means Va, FB,
100, the feedback means 10
0 includes a resistor 101 and voltage dividers 102 and 101 connected between the potential of the anode 51 and the ground potential. This high voltage feedback signal 105 is proportional to the potential between the anode 51 and the cathode 52 because the potentials of the anode and cathode are symmetrical with respect to the ground potential.

Feedback signal 9 proportional to anode current
5 is generated by the feedback means Ia, FB, 90. This means 90 is connected between the central inputs of the voltage doublers 40a, 40b. The DC component through these inputs is equal to the anode current of the x-ray tube. Capacitor 91 removes the AC portion of the current flowing through feedback means 90 through voltage dividers 92 and 93 where true feedback signal 95 is generated. A feedback signal 225 proportional to the output voltage 245 of the stabilizing means attached to the filament power supply is provided by the voltage divider 22.
Feedback means FR, FB, including 1,222
Occurs at 220. The height of the high voltage is influenced by the input voltage 115 of the pulse width modulator PWM,70. The pulse width modulator 70 and the pulse source 60a connected thereto are commercially available and well-known components. The same is true for pulse sources 60b and 60c. The pulse sources 60a, 60b and 60c may be formed into one pulse center, in which case the controllable section 20 and the DC-AC converters 30, 250 receive synchronized control pulses. X
The filament voltage of the wire tube and the associated anode current are determined by control signals from the controllable section 240. Comparators 110 and 120 and reference values Va, REF, 150 associated with the stabilization system consist of components whose high voltage power supply feedback signals 85 and 105 influence the generation of control signal 115. Comparator 110 includes an operational amplifier 111 and a feedback device 112. Comparator 120 includes an operational amplifier 121, a feedback device 122, and a resistor 123. The feedback signal 105, f ₂ of the outer control circuit is transmitted to the inner control circuit 70, 20,
80, H ₁ , F ₁ so as to follow up the differential signal 115, e of reference source 150, R.
A comparator 120 compares C 5 and r, and appears as an output voltage 125 of C ₂ . The anode voltage of the x-ray tube is thus adjusted so that the high voltage feedback signal 105 matches the value of the reference signal 155.

The control system for the filament power supply is of the same type as the control system for the high voltage power supply described above. It includes comparators 200 and 210 and a reference source.
Contains Ia, REF, 190. Comparator 200 includes an operational amplifier 201 and a feedback device 202.
Comparator 210 includes an operational amplifier 211, a feedback device 212, and a resistor 213. Similar to the high-voltage power supply, in the filament power supply, the feedback signal 95, f ₂ is transmitted to the inner control circuit 240, 22.
The differential signal 205, e of 0, H ₁ and F ₁ is influenced so as to perform follow-up control. The filament voltage is thus adjusted so that the anode current feedback signal 95 matches the value of the reference signal 195.

In the filament voltage control system,
Since the filament of the wire tube has a thermal time constant, the outer control circuit is determined to be appropriately delayed compared to the time constant of the inner control circuit by the feedback device 212, and the delay is set by the feedback device 202. .

Next, to explain the operation, when X-rays are emitted, the outer control circuit uses a fixed signal regardless of whether it is a high voltage control system or a filament voltage control system.
Since Vov, 140 and Vof, 180, r' are temporarily bypassed by switching signals 125 and 215, these fixed signals initially determine the values of high side voltage 26 and filament side voltage 245. After the switch is turned on, these signals 140,1
80 is a suitably selected time constant circuit Tv1 until voltages 26 and 245 are determined by the outer control circuit.
30 and TF, 170. When the switch is turned on, the contact 161 of the switch 160 is switched from the ground potential to a dedicated positive potential. Before the switch is turned on, the level of signal 125 is determined by the total voltage between diode 143 and diodes 142 and 141. When the switch is turned on, capacitor 132 starts charging through resistor 131 on one side, and resistor 123, diode 142,
It is charged through 143. capacitor 1
32 is sufficiently charged to operate switch 160, a reverse voltage is applied to diode 142, disconnecting diode 143 and capacitor 132 from the high voltage control circuit. diode 18
1, 182, 183, resistors 171, 213, and a capacitor 172 attached to the filament voltage control circuit are the capacitor 1 on the high voltage control circuit side.
32.

Here, the sequence of phenomena after the switch is turned on will be explained once again according to the timing graph shown in FIG. The anode voltage and the x-ray tube are switched on at timing T1 in FIG. Before that, the input voltage 125 of the operational amplifier 111, that is, the comparator 110, (V in FIG.
4) is locked to a value defined by diode 143. This means that the output voltage of the comparator 120 is
This is because the signal is temporarily bypassed by the switch 161 and the switch 161.

Then, the controllable unit 20 and the switch 161 are activated at the time T1 mentioned above to adjust the DC voltage 2.
6 (V5 in FIG. 5) rapidly rises to the voltage value defined by the output voltage 125, V4 of the comparator 120. The anode voltage proportional to this DC voltage 26, V5 also rises with a slight time delay.

After the above-mentioned timing T1, the capacitor 132 starts to be charged toward the potential V0 under a time constant determined by the resistor 131 and the capacitor 132. At this time, voltages V3 and V4 in FIG.
begins to rise at a similar slope. Its voltage V4,1
25 is stopped when the feedback signal 105, (V6 in FIG. 5) reaches the value of the reference signal 155, (V7 in FIG. 4). At this time, that is, at timing T2 in FIG.
The inner control circuit switches to be disconnected from the diode 143 control circuit and a steady state is reached.

In this steady state, ie after the initial switch-on, the inner control circuit is completely controlled by the outer control circuit. In this case, short-term stability and control are obtained by the characteristics of the inner control circuit, and long-term stability by the outer control circuit.

As described above, according to the present invention, the inner control system can be activated quickly to compensate for power supply frequency ripples and voltage fluctuations of the input voltage, and the outer control circuit can have a sufficiently slow time constant. This allows for stable control without overshoot. Moreover, by connecting the temporary reference signal to the inner control circuit bypassing the outer control circuit when the radiation source is activated, it is possible to speed up the rise of the system to the final balanced region.

The present invention is in no way limited to the above description, which is given by way of example only.
The specific content described above may vary within the scope of the invention as defined in the claims.

[Brief explanation of drawings]

FIG. 1 represents the control principle of the stabilization method of the invention, and FIG. 2 is a block diagram of an example in which the X-ray source intensity is stabilized by the method of the invention. FIG. 3 shows, corresponding to FIG. 1, how the high voltage and the filament voltage are created in the X-ray source and how the feedback is created, respectively.
FIG. 4 shows how the control signals are generated in the X-ray source of FIGS. 2 and 3. FIG. FIG. 5 is a timing graph showing changes in voltage values at various parts. (Explanation of symbols), 50... X-ray tube, 51... Anode, 52, 53... Cathode, 20,240
...Controllable unit, 115,205...Control input, 110,200...Comparator, 120,21
0...Other comparators, 105,95...Feedback signal, 100,90...Feedback circuit, 155,195...Signal, 150,190...
...signal source.

Claims (1)

[Claims] 1. A method for regulating the intensity of emitted X-rays from an X-ray source and stabilizing the intensity of the regulated emitted X-rays, which A first feedback signal is generated from the output of the controllable means for variably controlling the amount of electricity supplied to the X-ray source, and the first feedback signal and a reference signal corresponding to the desired amount of electricity to be supplied to the X-ray source are combined. forming an inner feedback control circuit for controlling said controllable means by means of a differential signal based on a comparison with a provisional reference signal set at a lower level than X;
A second feedback signal for controlling the anode voltage and/or filament voltage is generated from the anode voltage and/or filament voltage of the line source or a quantity proportional thereto, and the second feedback signal and the temporary reference signal are When the two values match, the inner feedback control circuit converts the signal to be compared with the first feedback signal from the provisional reference signal.
forming an outer feedback control circuit for controlling the anode voltage and/or filament voltage to be maintained at the reference signal by switching to a differential signal based on a comparison between the reference signal and a second feedback signal; The time constant of the control circuit is set to be smaller than the time constant of the outer feedback control circuit, and the anode voltage and/or filament is controlled by the inner feedback control circuit during initial operation and by the outer feedback control circuit during steady operation. A method for regulating and stabilizing the intensity of emitted X-rays from an X-ray source, characterized by controlling voltage. 2 Consists of an X-ray tube 50 including an anode 51 and cathodes 52, 53, a high voltage source, and a filament power source, and at least one of these power sources variably controls the amount of electricity supplied to the X-ray tube 50. variable control signals 115, 20 to these controllable parts 20, 240.
one input of the comparator 110, 200 forming the controllable part 20, 240 is coupled to the output of a feedback means 80, 220 which generates a first feedback signal 85, 225 from the output side of the controllable part 20, 240; A source of provisional reference signals 140, 180 and other comparisons where the other input of said comparator 110, 200 is set at a lower level than a reference signal 155, 195 corresponding to the desired amount of electricity to be supplied to said X-ray source. the other comparators 120, 210.
one input is coupled to the output of a feedback means 100, 90 for generating a second feedback signal 105, 95 from the amount of electricity applied to the x-ray tube 50 which is proportional to the output of the controllable part 20, 240. In addition, the other input of this comparator 120, 210 is a reference signal 15 proportional to the anode voltage.
5,195 and the second feedback signal 10 is coupled to the output of the source 150,190 of
5,95 coincides with the reference signal 155,195 output from the source 150,190, the other input to the comparator 110,200 is connected to the output of the source of the provisional reference signal 140,180. An X-ray device for regulating and stabilizing the intensity of emitted X-rays from an X-ray source, characterized in that it is configured to automatically switch from a coupled state to a coupled state with the outputs of the comparators 120 and 210. source. 3. A voltage regulator 20 is provided in the high voltage supply source that supplies the high voltage to the X-ray tube 50, one input of the comparator 110 forming the variable control signal 115 to the voltage regulator 20 is the output of the voltage regulator 20. via a first feedback circuit 80, and the comparator 11
0 is commonly coupled to a source of provisional reference signal 140 and to the output of another comparator 120 , one input of said other comparator 120 is coupled to a second anode 51 of x-ray tube 50 . and the other input of this other comparator 120 is coupled to the output of a source 150 of a reference signal 155 proportional to the anode voltage, the reference signal 155 being proportional to the anode voltage. signal 1
55 is set at a higher level than the provisional reference signal 140. 4. A controllable regulator 240 is provided in the filament voltage supply supplying the filament voltage to the cathode 53 of the X-ray tube 50, and one input of the comparator 200 forming the variable control signal 205 to the controllable regulator 240 is A first feedback circuit 22 is connected to the output of the controllable regulator 240.
0 and the other input of the comparator 200 is commonly coupled to the source of the provisional reference signal 180 and the output of the other comparator 210; is coupled to the voltage doubler 40a, 40b via a second feedback circuit 90, and the other input of this other comparator 210 is a source 190 of a reference signal 195 proportional to the desired anode current. 3. The X-ray source of claim 2, wherein the reference signal 195 of the source 190 is coupled to the output and sets the reference signal 195 of the source 190 to a higher level than the interim reference signal 180.